Insulated cable



Jan. 8, 1935. H, JOHNS ET AL 1,987,508

INSULATED CABLE Filed Feb. 7, 1951 Tic-.1.

Q uvsumrmm gmntozs Patented Jan. 8, 1935 UNITED STATES PATENT OFFICEOhio, asslgnors,

by mesne assignments, to Sterling Cable Corporation, a corporation ofMichigan Application February 7, 1931, Serial No. 514,240

9Claims In electrical installations it is well known that conductorsemployed for carrying currents, especially high tension and highfrequency currents, are open to the objection, which it has beendifficult to overcome, in that there is considerable electrostatic andelectromagnetic leakage, producing loss of current, corrosion of thecable, and other undesirable effects. This is apparently due to the factthat it is extremely dimcult to obtain perfect insulation and shieldingwithin reasonable limits of high tension current conducting cables, theleakage around such cables manifesting itself frequently as a staticfield, and being under certain conditions even visible as an area ofglow discharge in the vicinity of the conductor. The efl'ect is alsonoticeable through the production of ozone which manifests itself by itscharacteristic odor.

The glow discharge, commonly known as oorona, breaks down the insulatingproperties of the surrounding air, thereby rendering the air conductivein a well defined area. This discharge takes place when the criticalbreak-down voltage is exceeded and has many harmful and objectionableresults, among the most important of which are the 10$ of power, and thedeterioration of the insulation about the conductor through theoxidizing action of the ozone-containing atmosphere surrounding thecable.

It has now been discovered, however, that if the insulation of theconductor is itself covered with a flexible insulating coating carryingparticles of conductor material interspersed therethrough, that theformation of this static field around the conductor is avoided, theconductive coating applied to the insulation serving as a shield ordamper preventing such leakage. Experiments have also indicated that theshielding effect of such a coating is dependent upon-the quantity ofconductor material contained in the coating, the static field beingvirtually eliminated if there be sufilcient particles in the coating toform a continuous layer with no open interstitial spaces between theconducting particles.

It appears that the best results are obtained by using as the flexiblecoating medium, nitrocellulose lacquers carrying metal powders orpowdered graphite, as the pigment for the lacquer. For example, if theinsulation on the cable is coated with such a lacquer carrying asufllcient quantity of powdered aluminum to present a uniformly silveredappearance, the shielding effects will be very satisfactory, so that theconductors so insulated may be safely employed in the electrical systemsof automobiles for example, without danger of the deleterious electricaleffects now very often experienced, especially if by any chance watershould come in contact with the cables. Furthermore, the utilization ofaluminum powder as a shielding medium is very desirable since it impartsa distinctive color to the cables, and since the aluminum is notaifected as to its color by contact with the sulphur in the rubberinsulation, the use of the aluminum will render the appearance of thecable permanent and free from tarnish. While aluminum is preferred, itwill be understood that any other metallic powder such as bronzepigments for example can be employed to produce a shielding effect, andalso powdered graphite may be employed for the same purpose. Theshielding effect of the conductive particles is apparently enhanced bythe microscopic film of lacquer which surrounds each individual particleof the conducting material; and since the lacquer employed is veryelastic, the cables can be bent in any desired manner without danger ofbreaking the lacquer coating.

The invention will be more readily understood by reference to theaccompanying drawing, in which- Figure 1 represents in elevation afragment of an insulated cable provided with the conductor carryingcoating such as above described.

Figure 2 is a longitudinal section through the cable and its surroundinginsulation showing the additional coating applied to the usualinsulation, taken on the line 2-2 of Figure 3, and

Figure 3 is a cross section of the improved cable taken on the line 3-3of Figure 1.

Referring more particularly to the drawing, 10 represents the conductingcable provided with the usual insulation 11, the insulation 11 beingsurrounded by the usual cotton fabric braid 12, which braid may or maynot be covered with a thin layer of insulation. The insulation 11 isusually the conventional rubber insulation. Applied to this braid 12 inaccordance with this invention is the additional external layer 13,which layer carries thickly interspersed therein conductive particles soas to give a uniformly appearing surface.

This layer 13 is applied, as above mentioned, by applying in any wellknown manner to the insulation 11, a lacquer formed of a nitro-cellulosebase in a suitable solvent and carrying as its pigment particles ofpowdered aluminum, powdered graphite, or bronze, or any other goodconducting material so that there will be presented a homogeneousappearance when the lacquer coating has dried on the cable; and exceptfor a microscopic layer of the lacquer surrounding each particle, theindividual particles of the conductive powder are in substantiallyunbroken contact with each other.

Aluminum is the preferred material for use as the shielding substance,since it imparts a permanent characteristic appearance to the cable,

I whereas other materials such as bronze, may tarnish in time throughthe action of sulphur contained in the rubber insulation. However, theshielding effect of these various conductors is good, one of theessential factors for electrostatic shielding being that the materialpossesses high electrical conducting properties; graphite is found to bevery effective, although, of course, it does not present anyparticularly characteristic appearance. The lacquer coating beingelastic will conform to any curvature imparted to the cable withoutbreaking, so that an efiective shielding action is obtained, which isespecially desirable in the electrical circuits of automobiles, forradio circuits, and for shielding radio apparatus from the effects ofhigh tension currents, as for instance where the apparatus is installedin automobiles. It has also been found that when the present cable isemployed in the wiring systems of automobiles or elsewhere where thecables are exposed to the action of oil and heat, the ductility andflexibility of the lacquer film is increased by the presence of themetal particles; and this is true whether the lacquer has beenplasticized by resin or by oil. This action appears to result from achemical reaction between the plasticizers or the gum content of thelacquer and the metal, leaving the film together and less brittle afterit is subjected to the effects of heat and oil. By varying the amount ofmetal in the lacquer film, various degrees of flexibility can beproduced.

The metal coating may be applied in various ways, for instance, bysuspending the powder in the lacquer as a pigment; or the metallic filmcan be sprayed on the surface of the insulated cable immediately afterit has received a coat of lacquer, there being thereby produced a smoothand even film, the metallic particles clinging to the lacquer surface asthe lacquer dries. It is to be understood that the term lacquer as usedin the specification and claims means a lacquer which includes anitro-cellulose base or the equivalent thereof in a suitable solvent.

It will be apparent that variations in the specific details of thisinvention may be made without departingfrom the inventive concept. Itwill be understood, accordingly, that it is intended to embrace withinthe scope of this invention such modifications and changes as may benecessary to adapt it to varying conditions and uses.

Having thus described our invention, what we claim as new and desire tosecure by Letters Patent of the United States, is

1. An insulated electrically conducting cable having applied thereto anexterior coating comprising a cellulose lacquer having uniformlyinterspersed therein a finely divided electrically conductive material,the individual particles of which are separated by thin layers oflacquer,

and the conductive material being in such proportion as to provide aconductive static and ma netic shield about the cable.

2. An insulated cable for use in high tension electrical circuits,having applied thereto a coat- 5 ing of finely comminuted electricallyconducting material interspersed in a cellulose lacquer, thecharacteristic of said lacquer being such as to render the coatingflexible, and the conducting material having its particles separated bylayers of lacquer of microscopic thickness, but being present in suchquantity to provide a conductive static and magnetic shield about thecable.

3. An insulated electric cable provided with a homogeneous coating of aconductive powder carried by a cellulose lacquer, the individualparticles of the powder being separated by films of the lacquer, butbeing present in such quantity to provide a conductive static andmagnetic shield about the cable.

4. An electrical conductor cable comprising a conductor, a layer ofinsulation surrounding the conductor, a braid surrounding theinsulation, and a shielding coating comprising finely divided aluminumcarried by a cellulose lacquer applied to 25 the braid and forming asubstantially continuous sheath of even thickness serving as aconductive shield against electrostatic and electromagnetic fields.

5. An electrical conductor cable comprising a 30 conductor, a layer ofinsulation surrounding the conductor, and an elastic coating on saidinsulation comprising a cellulose lacquer having interspersed thereinfinely comminuted electrically conductive material, the said conductivematerial 35 being in such proportion as to increase the flexibility ofthe elastic coating when subjected to heat and providing a conductivestatic and magnetic shield about the cable.

6. In an electrically conducting cable having 40 insulation thereabout,a coating of cellulose lacquer extending about said insulation andcarrying finely divided electrically conductive material in suchproportion to form a conductive static and magnetic shielding layer.

7. In an electrical cable having insulation thereabout, a coating ofcellulose lacquer extending about said insulation and carrying finelycomminuted aluminum in such proportion to form a conductive static andmagnetic shielding layer.

8. A sheath for electric conductors having a coating of celluloselacquer with metallic powder incorporated therein, the individualparticles of the powder being separated by films of lacquer but beingpresent in such quantity as to provide a conductive static and magneticshield about the cable.

9. A flexible sheath for insulated electric conductors, comprising acoating with metallic powder interspersed therein in sufiicient quantityto produce an electrical shielding effect, said coating being of asubstance which protects the metal particles and is resistant to attack.by oil, gasoline or the like.

HAYS JOHNS.

VERNE F. DOBBINS.

